UK businesses are among those counting the costs of the Slammer worm that hit computers over the weekend.

The virulent worm crippled online traffic and affected an estimated quarter of a million computers worldwide.

At the moment the internet is recovering from its sticky cheese fondue state

Graham Cluley, Sophos

SQL Slammer targeted a known flaw in Microsoft's database software affecting servers rather than home computers.

The incident, which experts say has been the most damaging net attack in 18 months, shut down many of the servers which run websites around the globe.

Pants down

Cheshire-based Midnightexpress Lingerie Ltd was just one of the UK businesses to be affected by Slammer.

The Midnightexpress website went down at around 0500 GMT on Saturday and was offline until 1600 GMT in the afternoon.

"It was a damn nuisance and ironic that it struck on the same Saturday that we had launched an advertisement campaign for Valentine's Day in the national press," Managing Director John Vincent told BBC News Online.

"People would have gone to look at the website and it wouldn't have been there. It is likely that they won't bother going back," he added.

Who's to blame?

Mr Vincent estimates that his firm alone has lost thousands of pounds worth of business but believes that getting compensation is unlikely to be easy.

"As it is an international virus, ISPs will probably have some form of disclaimer," he said.

He acknowledges that his own ISP Mistral did all they could to get the site back up and wonders if the blame really lies with the makers of the software, Microsoft.

"It is difficult to lay the blame at anyone's door. It all comes back to Bill Gates as usual," he said.

Cheese fondue

Anti-virus firm Sophos is currently running a poll to ascertain whether users will blame Microsoft or the systems administrators who failed to provide adequate patches for the flawed software.

"To Microsoft's credit they told people about the bug six months ago and ultimately it may be that systems administrators need to buck up their ideas and take security more seriously," said Sophos' Senior Technology Consultant Graham Cluley.

The internet meltdown experienced by many over the weekend does appear to be over now, he said.

"At the moment the internet is recovering from its sticky cheese fondue state and becoming the rapidly moving liquid we all expect it to be," he said.

Other UK firms hit by Slammer included Hewlett Packard, Borders.co.uk, Letsbuyit.co.uk and Thorntons.co.uk.